Prevention of hypertension will come only when we understand the basic mechanisms regulating blood pressure. Work in many laboratories have established that among the numerous mechanisms of blood pressure regualtion are, cardiopulmonary reflexes, arterial baroreceptor reflexes, the renin-angiotensin-aldosterone system, the antidiuretic hormone, and prostaglandins. In the proposed project, trained unanesthetized animals and selected in vitro preparations will be used both for the study of individual regulatory mechanisms and for the study of the way these mechanisms interact. Thus the experimental approach will range from characterization of blood pressure responses in unanesthetized dogs to the quantification of transport ATPase in identified single renal tubules. The proposed investigations will include: 1. The interaction of cariopulmonary, arterial and renal receptors in the regulation of renin secretion, antidiuretic hormone secretion, and the control of blood pressure in the trained unanesthetized, conscious dog. 2. Determination of the pathogenesis of the malignant hypertension induced by mild renal artery constriction. 3. Localization and quatitation of dopamine and other catecholamines in kidneys from dogs with varying salt intakes and with renovascular hypertension. 4. Definition, in diabetes insipidus rats, of the relationships between antidiuretic hormone, the renin-angiotensin-aldosterone system, and renal prostaglandin synthesis. 5. Definition of the distribution activity of Na-K-ATPase in renal tubule segments in response to adrenalectomy, salt state, and renovascular hypertension.